The present invention relates to an optical information reproduction device. More specifically, this invention relates to a device for optically reproducing information from a disk medium on which concentric or spiral tracks are disposed, the medium comprising identification information areas in which identification information representing address information and the like are shifted radially inward and radially outward each approximately by a predetermined distance with respect to a track center and user information areas in which user information and the like are recorded on the center of a track.
In recent years, it has been demanded that a memory means for storing information store image information, video information, and other voluminous information in comparison with the conventional textual information and sound information, and optical disks have been attracting attention as a response to the demand. Conventional recordable optical disks are provided with guide grooves formed at the time of the production of the disk. The guide grooves are used to keep the light beam for recording and reproduction in the center of a track. These guide grooves result in convex areas (lands) and concave areas (grooves) formed in spiral or concentric form on the disk. The disk using both the convex areas and concave areas as recording tracks (land tracks and groove tracks) can record twice as much information as a disk using either areas as recording tracks. This method is referred to as a land/groove recording method and is described in Japanese Patent Application Kokoku Publication No. 57859/1988.
A recording track is generally divided into sectors in the direction of the track, and in each of the sectors, identification information, such as a track number, and a sector number, is preformatted as physically formed convex and concave pits. The identification information is disposed in either of these methods: In one method, dedicated identification information for a land track or groove track is disposed; in another method, the information is disposed in a position shifted in a radial direction so that the information can be shared by a land track and a groove track adjacent to the land track, more specifically, along the boundary between a land track and a groove track.
The former method in which exclusive identification information is disposed in each track enables track-specific information to be included, making it easy to control the device. In the mastering of this type of disk, the pit width needs to be sufficiently narrower than the track pitch. It is therefore difficult to form desired pits with the same laser beam as that used for forming guide grooves. Thus, disk production process is complicated.
In the latter method of sharing identification information by a land track and a groove track adjacent to the land track, the device needs to judge which track is being reproduced because two tracks share the identification information, and the control is a little more complicated than that for the former exclusive disposition method. However, the same laser beam as that used for forming guide grooves can be used for pre-formatting the identification information in mastering, which can be done by deflecting the laser beam in a radial direction just by 1/4 of the distance between the centers of the adjacent lands, by the use of a light deflection means. This type of optical disk and an optical information reproduction device using such optical disks are disclosed in Japanese Patent Application Kokai Publication No. 176404/1994.
An optical information reproduction device using an optical disk on which identification information is disposed in the latter method will next be described. FIG. 7 shows the track format of the conventional optical disk. FIG. 8 shows how the conventional identification information portion is disposed. FIG. 9 is a block diagram showing the configuration of the optical information reproduction device for reproducing information from that type of optical disk.
In FIG. 7 and FIG. 8, reference numeral 1 denotes an identification information area in which identification information is preformatted; reference numeral 2 denotes a user information area In which user information is recorded by means of a variation in the local optical constant or physical shape; reference numeral 3 denotes a groove track; and reference numeral 4 denotes a land track. As shown in the figures, the groove track 3 or land track 4 is disposed in spiral form in the full circumferential extent, and the tracks are divided into sectors in the direction of the tracks. A sector includes, at the beginning, the identification information area 1 in which information for identifying the sector, such as the track number and sector number is recorded, and the identification information area 1 is followed by the user information area 2 for recording user data and the like. The identification information is shared by the land track 4 and the groove track 3 adjacent to the land track, and the displacement of the identification information from the track center of the land track 4 or groove track 3 is 1/4 of the distance between adjacent land tracks 4 or of adjacent groove tracks 3.
The configuration of the conventional optical information reproduction device will next be described with reference to FIG. 9. In the figure, reference numeral 11 denotes an optical disk; reference numeral 12 denotes a spindle motor; reference numeral 13 denotes an optical head; reference numeral 14 denotes a first current-to-voltage (I/V) converting means; and reference numeral 15 denotes a second I/V converting means.
An adding means 16 adds the output of the first I/V converting means 14 and the output of the second I/V converting means 15.
A sum signal detecting means 17 detects the information recorded on the disk by processing and then converts the output (a) of the adding means 16 into binary values.
A subtracting means 18 obtains a difference between the output of the first I/V converting means 14 and the output of the second I/V converting means 15.
A polarity reversing means 19 reverses the polarity of the output waveform (b) of the subtracting means 18 according to the control signal from a controller 26, which will be described later.
A difference signal detecting means 20 detects the information recorded on the disk by processing and then converts the output (d) of the polarity reversing means 19 into binary values.
A signal selecting means 21 selects the output (c) of the sum signal detecting means 17 or the output (e) of the difference signal detecting means 20 according to the control signal (f) from a control gate generation means 25, which will be described later.
A clock generation means 22 generates the reproduction clock (CK) in synchronization with the output (g) of the signal selecting means 21 according to a control gate signal (RG) from the control gate generation means 25.
A data demodulating means 23 judges whether the output (g) of the signal selecting means 21 is at level "1" or "0" at the timing of the reproduction clock from the reproduction clock generation means 22 and demodulates the data.
An address information reproduction means 24 reproduces an address after reproducing identification information by judging at the timing of the reproduction clock from the reproduction clock generation means 22 whether the output (g) of the signal selecting means 21 is at level "1" or "0".
The control gate generation means 25 generates the control gate signal mentioned earlier, with reference to the timing of the address reproduction completion signal from the address information reproduction means 24.
The controller 26 outputs a control signal to the polarity reversing means 19 according to the address information from the address information reproduction means 24.
The optical head 13 comprises a laser diode (LD) 131, a collimate lens 132, a beam splitter (BS) 133, a converging lens 134, and a photodetector (PD) 135.
The operation of a prior-art optical information reproduction device configured as described above will be described with reference to FIG. 9 and FIG. 10A to FIG. 10H. FIG. 10A to FIG. 10H show waveforms at various points in FIG. 9.
When the optical disk 11 is placed, by a mechanism, not shown, on the spindle motor 12, the controller 26 sends a spindle activation signal and speed information, which are not shown, to a rotation controlling means, which is not shown, to adjust the spindle motor 12 to a predetermined speed. Then, the laser diode 131 of the optical head 13 is turned on by a lighting command, which is not shown, from the controller 26. The output of the laser diode 131 is kept to a constant value by a feedback controlling means, which is not shown.
The collimate lens 132 converts the laser beam emitted from the laser diode 131 into parallel rays of light, which pass the beam splitter 133 and are converged onto the optical disk 11 by the converging lens 134. After passing the converging lens 134, the far field pattern of the light reflected from the optical disk 11 (return light), which includes the information component on the optical disk 11, is reflected by the beam splitter 133 and projected onto the photodetector 135. The photodetector 135 has at least two light-receiving parts which are disposed on opposite sides (radially outward and radially inward sides) of a track tangential line in the projected far-field pattern, i.e., of a track tangential line in the far field of the information pits on the optical disk 11. In this connection, the optical system for passing the light beam from the laser diode 131 in the optical head 13 to the surface of the optical disk 11, and passing the light reflected at the surface of the optical disk 11 to the photodetector 135 is so designed that the center of the far field pattern of the information pits on the optical disk 11 is formed at the boundary between the two parts of the photodetector 135.
The optical system of the optical head 13 is adjusted so that the position of the beam spot in the radial direction can be controlled through the use of the light distribution information on the two-part split photodetector 135.
When the beam spot is in the center of a track, identical amounts of light strike the two parts of the split photodetector 135, and the difference between the two outputs, that is a push-pull signal, is zero. As the beam spot goes away from the center of the track, the distribution of light on the two-part split photodetector becomes unbalanced, increasing the value of the push-pull signal. The value of the push-pull signal is zero when the beam spot is in the center of the land track 4 or groove track 3, and the value is maximized or minimized when the beam spot is on the boundary between the land track 4 and groove track 3.
Tracking to keep the beam spot in the center of a track can be performed through feedback control to set the difference between the output signals from the two-part split photodetector 135 to zero. This technique is commonly utilized as a tracking method for optical disks having guide grooves.
The light reflected from the optical disk 11 (return light) including the information component on the optical disk 11, which is mentioned above, is converted into current signals by the photodetector 135, which are then converted into voltage signals by the first I/V converting means 14 and the second I/V converting means 15 in the subsequent stage. By obtaining the difference between the voltage signals at the subtracting means 18, a tracking error signal can be obtained in the push-pull method mentioned above. Using this signal, a tracking control means, which is not shown, performs control so that the beam spot always scans the center of a track.
As for displacements in the direction of the optical axis of the light beam such as undulation of the surface of the disk, a focus controlling means, which is not shown, performs control to keep the beam spot converged onto the optical disk 11.
With the beam spot controlled by the controlling means mentioned above, the information on the optical disk 11 is read. Information is recorded onto the optical disk 11. The following description is limited to the reproduction of the information.
The voltage signals from the first I/V converting means 14 and the second I/V converting means 15 are added by the adding means 16 to form a waveform as shown as (a) in FIG. 10A. The output from the subtracting means 18 mentioned above has a waveform as shown as (b) in FIG. 10C or (b') in FIG. 10D when the beam spot is at the center of a track. Whether the waveform is like (b) or (b') depends on whether the position of pits in the identification information area 1 is shifted radially inward or radially outward with respect to the center of the land track 4. Since the beam spot is at the center of the track in the user information area, the outputs from the two parts of the split photodetector 135 are the same, and the output of the subtracting means 18 is 0 (or a reference level).
Suppose the light beam is scanning pits in the identification information area which are shifted radially inward with respect to the center of the land track. If the outputs from the two I/O converting means are connected to the subtracting means 18 in such a manner that the signal reproduced from the identification information area has the waveform as shown as (b) in FIG. 10C when the land track of the optical disk 11 is reproduced, the signal reproduced from the identification information area in the groove track reproduction has a waveform as shown as (b') in FIG. 10D. The reverse also holds.
When the information on the optical disk 11 is reproduced according to the output of the adding means 16, the analog signal output from the adding means 16 is judged to be larger or smaller than a predetermined slice level (Vth1) and is converted into binary values by the sum signal detecting means 17 and has a waveform as shown as (c) in FIG. 10B.
The reproduction of the identification information in the identification information area 1 on the optical disk 11 according to the output from the subtracting means 18 will next be described. This method is disclosed in Japanese Patent Application Kokai Publication No. 176404/1994.
The polarity of the reproduction waveform of the analog signal output from the subtracting means 18 differs depending on whether the reproduced track is a land track or a groove track, as described above. Generally, the level slicing means that produces binary values by slicing the analog waveform is designed with the polarity of input signal fixed. A system In which the polarity of the reproduced waveform changes therefore requires the polarity reversing means 19 to provide a signal of a fixed polarity.
The polarity reversing means 19 can be easily controlled if the relationship between the track and the polarity of the reproduced waveform is known beforehand. That is, the controller 26, which will be described below, may operate the polarity reversing means 19 by judging whether the sector being scanned is on the land track or groove track. As a result, as shown as (d) in FIG. 10E, the polarity of the reproduced waveform of the identification information is maintained, irrespective of whether the sector being scanned is in the land track or groove track. In the shown example, the waveform is kept below the reference level. The output of the polarity reversing means 19 is converted into binary values by the difference signal detecting means 20, resulting in the waveform as shown as (e) shown in FIG. 10F.
The method of reproducing the identification information such as a track address and sector address and the user information such as user data from binary signals will next be described. It is incidentally noted that "user information" includes data used for phase-locked loop pulling-in, synchronization pattern, error-detection and correction codes, as well as "user data".
First, if the identification information and user information are reproduced through the use of the output (c) of the sum signal detecting means 17, the signal selecting means 21 is set to always select the output (c) of the sum signal detecting means 17.
If the output (e) of the difference signal detecting means 20 is used to reproduce the identification information and the output (c) of the sum signal detecting means 17 is used to reproduce the user information, the signal selecting means 21 accordingly switches to select the desired signal. The switching of the signal selecting means 21 is made according to the switching signal (f) (shown in FIG. 10G) from the control gate generation means 25, which will be described later. The switching signal is generated by an internal timer or the like, which is started by a timing signal which can identify a known position within a sector, such as the address detection completion timing signal from the address information reproduction means 24.
The output (g) of the signal selecting means 21 is supplied to the reproduction clock generation means 22, the data demodulating means 23, and the address information reproduction means 24.
The reproduction clock generation means 22 generates the reproduction clock in synchronization with the output signal (g) from the signal selecting means 21, using a phase locked loop (PLL) means. The reproduction clock generation means 22 is designed to operate within the area in which the information to be reproduced is present, according to a read gate signal (RG) from the control gate generation means 25.
The address information reproduction means 24 reproduces the identification information by checking at the timing of the reproduction cloak from the reproduction clock generation means 22 whether the output signal (g) from the signal selecting means 21 is at "1" or "0", and thereby detects an address.
The data demodulating means 23 demodulates data by checking at the timing of the reproduction clock from the reproduction clock generation means 22 whether the output signal (g) from the signal selecting means 21 is at "1" or "0" and then performs decoding, error correction, and de-interleaving.
The control gate generation means 25 generates the switching signal (f) (shown in FIG. 3I) of the signal selecting means 21 and the read gate signal (RG) (shown in FIG. 3J, to be supplied to the reproduction clock generation means 22) according to the internal timer, started at the address detection completion timing (shown in FIG. 3H) provided by the address information reproduction means 24. The address detection completion timing is a timing when the decoding of the address having been read from the identification information area is completed. In the drawing, it is shown to be immediately after the end of the identification information area.
The controller 26 identifies the sector from which information is being reproduced according to the address reproduced by the address information reproduction means 24 and the information indicating whether information is being reproduced from a land track or a groove track, which is obtained from the tracking control means. If the track from which information is to be reproduced is changed at an access or on other occasions, the controller judges whether the track containing the target sector is the land track or groove track and outputs a control signal for setting the polarity of the output signal to the polarity reversing means 19. In addition, the controller 26 controls the whole device, which is not shown.
As described above, because the identification information is disposed between a land track and a groove track, being shifted from a track center, the identification information can be reproduced and detected regardless of whether the beam spot is scanning a land track and a groove track. Because the identification information need not be separately formed for the land track and for the groove track, the number of processes in optical disk mastering can be reduced.
However, because identification information is shared by a land track and a groove track, as described above, it is hard to identify a sector Just by reproducing the address, and the information indicating whether information is being reproduced from a land track or a groove track is additionally required.
Because the identification information is shifted from a track center, any track offset of the beam spot in a radial direction away from the identification information causes the amplitude of the signal reproduced from the identification information to be degraded, reducing the address detection accuracy. A low address detection accuracy will result in a low recording reliability or a low reproduction reliability.
In addition, it is hard to identify whether the track from which information is being reproduced is a land track or a groove track Just by detecting the identification information.
Further, because the identification information and user information are separately detected, the scale of the circuit is large.
To solve these problems, an optical disk with the identification information disposed in a staggering manner as shown in FIG. 11 is provided. A feature of this disposition is that identification information is split into two areas and that the information of one area (hereafter referred to as the first identification information) is shifted by a predetermined distance radially outward with respect to the track center, and the information of the other area (hereafter referred to as the second identification information) is shifted by a predetermined distance radially inward with respect to the track center and radially inward with respect to the center of the track. The amount of shift is preferably about 1/2 of the track pitch.
If this identification information is used for tracking control, the tracking offset can be canceled. That is, when the first identification information and second identification information reproduced by the subtracting means mentioned above have the same reproduction amplitude, the beam spot is judged to be at the center of the track.
Based on the order of detection in which the first identification information area and the time at which the second identification information area are detected, the track on which the beam spot is scanning can be known. That is, when the beam spot is scanning a land track, the first identification information (shifted radially outward) is detected, and then the second identification information (shifted radially inward) is detected. When the beam spot is scanning a groove track, the second identification information (shifted radially inward) is detected, and then the first identification information (shifted radially outward) is detected. Through the use of this relationship, whether the track from which the information is being reproduced is in a land track or in a groove track can be judged, and the sector can be identified just by reproducing the identification information.
The conventional optical information reproduction device as described above with reference to FIG. 8, however, is designed on the assumption that the identification information is shifted in only one direction with respect to the track center, and the polarity reversing means can be controlled just in units of tracks, that is, the polarity is switched not switched until the end of each land track or each grove track. With this configuration, it is impossible to control the signal polarity for each piece of identification information. Accordingly, if the conventional optical information reproduction device is used to reproduce information from an optical disk as shown in FIG. 11, Just the output of the adding means can be used to detect the identification information, and the push-pull signal output from the subtracting means cannot be used. In this case, the first identification information and second identification information cannot be separately detected, and whether the track from which information is reproduced is a land track or a groove track cannot be judged solely from the detected identification information.
Moreover, a judging means, such as one which makes judgment by evaluating the accuracy or reliability of address detection, for deciding which of the outputs from the adding means and subtracting means is to be used for reproduction of the identification information is not available, and the address detection accuracy may therefore be degraded.